Danio annulosus, Kullander, Sven O., Rahman, Md. Mizanur, Norén, Michael & Mollah, Abdur Rob, 2015

Kullander, Sven O., Rahman, Md. Mizanur, Norén, Michael & Mollah, Abdur Rob, 2015, Danio annulosus, a new species of chain Danio from the Shuvolong Falls in Bangladesh (Teleostei: Cyprinidae: Danioninae), Zootaxa 3994 (1), pp. 53-68 : 56-60

Danio annulosus , new species

( Figs. 1 a–b)

Holotype. DU 50001, adult, probable female, 71.5 mm SL; Bangladesh: Chittagong Division, Rangamati District, Borokal, pool at bottom of Shuvolong Waterfall. M. M. Rahman, S. O. Kullander, M. Norén, A. Obaida, M. Hossain and M. Rashid, 28 Nov 2014.

Paratypes. NRM 67114, 4, 50.1–68.2 mm SL; NRM 66255, 1, 45.8 mm SL; DU 60001, 4, 41.8–50.7 mm SL. Same data as holotype.

Diagnosis. Distinguished from all other species of Danio except D. assamila , D. dangila , D. catenatus , D. concatenatus , and D. sysphigmatus by produced first ray in pectoral and pelvic fins, large cleithral spot, and pattern of dark rings enclosing light interspaces on the side. Distinguished from those species by slightly horizontally extended cleithral spot (vs. vertically extended in D. dangila , round in the other species), anterior interstripe Ia usually present (vs. absent in D. dangila and D. catenatus ), rings in series along side elongate, width of each dark ring of about same as diameter of light centre or wider (vs. elongate, with narrower dark ring in D. sysphigmatus , round or slightly elongate and with dark ring about as wide as light centre in other species), ring pattern usually not extending onto caudal peduncle (vs. present on part of caudal peduncle in D. dangila , D. catenatus and D. concatenatus ), lateral-line scale count 34–35, (vs. 35–38 in D. sysphigmatus ), pectoral fin barely or not reaching to base of pelvic fin, unbranched leading ray only slightly longer than remaining rays (vs. leading ray prominently elongated, reaching to base of unbranched pelvic-fin ray or beyond) ( Figs. 1–2 ), pelvic fin without produced unbranched ray, not reaching to vent (vs. with unbranched ray distinctly longer than the rest, and reaching to vent or bases of anterior anal-fin rays) ( Figs. 1–2 ).

Description. General body features and pigmentation are illustrated in Fig. 1 . Measurement data are summarized in Table 2 .

Body compressed, moderately elongate to moderately deep, no sexual dimorphism evident. Head compressed, about as wide as deep. Snout short, rounded in lateral view, length about equal to eye diameter. Mouth terminal, oblique in profile, lower jaw slightly projecting. Small bony knob at dentary symphysis, fitting into notch in upper jaw. Maxilla reaching to vertical from anterior margin of orbit. Lower jaw ending anteriorly at about middle of eye. Lower jaw with pointed anterior lateral lobe. Tubercles absent from lower jaw or present in a row along lateral margin of dentary and/or a few small tubercles anteriorly. Rostral barbel reaching little past preopercle, at most to vertical at middle of opercle. Maxillary barbel long, reaching to middle of base of pectoral fin or slightly posterior to base of pectoral fin.

Lateral line complete, comprising 34* (1), 35 (9) scales; descending anteriorly for about 6 scales, from some of which pores are absent, posteriorly paralleling ventral profile. Median predorsal scales 16 (1), 17* (7), 18 (2). Scales in transverse series from dorsal-fin origin to pelvic-fin origin ½6+1+1½* (10); scales below lateral line much smaller than above. Prepelvic scales about 14–17 along prepelvic midline; pelvic-fin bases covered by overlapping scales arranged in three rows. Circumpeduncular scale rows 14* (10). Pelvic axillary scale present. A row of scales along anal-fin base.

Dorsal-fin rays ii.9 ½ (2), ii.10 ½ (6), ii.11 ½* (2); anal-fin rays iii.13 ½ (1), iii.14 ½* (6), iii.15 ½ (3); pectoral-fin rays i.12 (4), i.13 (6), including 1–2 minute unbranched ventral rays; pelvic-fin rays i.7 * (10). Principal caudal-fin rays 10+9 (7); procurrent caudal-fin rays dorsally 5 (2), 6 (2) 7 (2), ventrally 5 (1), 6 (4). Dorsal fin inserted at highest point of dorsum, slightly posterior to half distance from snout tip to caudal-fin base, distinctly anterior to vertical from anal-fin origin. Pectoral-fin insertion at about vertical through posterior margin of opercle; branched rays forming slightly rounded or subtruncate margin, leading unbranched ray produced beyond rest of fin, just reaching base of unbranched pelvic-fin ray (68.2 mm specimen only, Fig. 2 ) or shorter. Tubercles present on pectoral fin on 2nd to 4th or 5th branched ray in three paratypes (50.1, 50.7, 68.2 mm SL). Pectoral-fin axial lobe well developed. Pelvic-fin origin situated slightly anterior to midbody, well anterior to dorsal-fin origin. Pelvic-fin margin slightly rounded or truncate, leading unbranched ray only slightly longer than remainder, not reaching vent. Caudal fin slightly emarginate, lobes about equal, lobe tips subacuminate or rounded.

Vertebrae 17+18=35 (1), 17+19=36 (4), 18+17=35 (1), 18+18=36 (1); predorsal vertebrae 14 (7); vertebrae contained within caudal peduncle 5 (1), 6 (4), 7 (2). Ceratobranchial 5 tooth formula 2,4,5-5,4,2 (NRM 66255).

Colouration in preservative. Description based on specimens fixed in formalin and transferred to ethanol ( Fig. 1 b, c). Specimens initially preserved in 95% ethanol similar but with white semi-transparent overlay ( Fig. 1 a). Ground colour fawn or dull yellow, ventral midline white, head pale grey. Markings absent from head and venter, except slight concentration of dark pigment adjacent to lower margin of orbit and centre of opercle. Dorsal midline anterior and posterior to dorsal fin marked by narrow dark-brown stripe. Dark brown or grey stripes P, P+1, P+2, P- 1, P-2; P+3 stripe absent. Cleithral spot black, slightly longer than deep (depth 70–96% of length, mean 77%, N=10), about as large as pupil. P+ stripe expressed as small round spots and short lines in irregular row from above upper end of gill cleft to root of caudal peduncle. P+1 and P stripes distinct on caudal peduncle, where forming straight parallel stripes, ending on scaled base of caudal fin; anteriorly anastomosing, contributing to a row of 4–10 contiguous elongate dark rings enclosing interstripe I. P-1 stripe distinct, narrow posteriorly, paralleling posterior parts of P and P+1 stripes, but ending in upward slant on basal scales of caudal fin; for most of extent anastomosing with lower branch of P stripe to form 4–7 large elongate rings fragmenting interstripe I-1; ring pattern irregular anteriorly on side with occasional absent ring parts. Narrow interstripe Ia inserted between dorsal and ventral rows of rings, expressed as subcontinuous stripe or irregular circle centres, extending from below cleithral spot to about vertical from anterior anal-fin rays. P-2 stripe indistinct, undulating, narrow, originating at pectoral-fin base, ending above posterior part of anal-fin base. Dorsal fin hyaline basally; dark interradial spots proximally forming dark stripe close to base; distally wide grey zone margined with darker grey on about middle of fin (D stripe); wide distal margin white. Anal fin hyaline basally; dark interradial spots forming dark stripe at base; dark interradial spots forming dark stripe (A-1 stripe) marking about proximal third of width of fin; outer two thirds of fin pale grey, margined by darker grey A stripe, distal margin of fin white anteriorly. Caudal fin dusky, lighter along middle, with distinct dark stripes or series of spots continuing stripes P+1, P and P-1. Sexual dimorphism absent in colour pattern.

Colouration in life. Freshly captured specimens had same colour pattern as preserved specimens. Dark stripes (including circles) were blue and interspaces (including circle centres) were orange. A distinct orange spot anterior to black cleithral spot. Some of orange colour remaining for some time in preserved specimens ( Fig. 1 c).

Geographical distribution and habitat ( Figs. 3–5 ). Danio annulosus is so far known only from the type locality at the foot of a waterfall draining into the Kaptai Lake. The Kaptai Lake is a reservoir formed by the damming of the Karnafuli River, completed in 1962. In the wet season, the fall has a height of about 100 m and falls directly into the lake. At the time of collecting, the lake level was low: the waterfall had almost ceased and only some dripple moistened the rock. Water was retained in a small pool at the foot of the fall, at most about 40 cm deep, holding some pieces of rock but devoid of vegetation. Specimens were seined from the deeper shadowed area of the pool along with numerous specimens of shrimp, snails, and a small species of Garra Hamilton. The pool drained to the lake by a small stream, only about 1 cm deep. Seining in the lake at the mouth of the stream yielded Esomus danrica (Hamilton) , Rasbora daniconius (Hamilton) (Cyprinidae) , Dermogenys burmanica Mukerji (Zenarchopteridae) , Aplocheilus panchax (Hamilton) (Aplocheilidae) , and Trichogaster lalius (Hamilton) (Osphronemidae) , which are ubiquitous species in Bangladeshi freshwaters.

Etymology. The species name, annulosus , is a Neolatin adjective meaning ringed, inspired by the colour pattern on the side, which resembles series of dark rings.

Comparative morphometrics. Danio annulosus has slightly shorter pectoral and pelvic fins ( Fig. 6 a–b, shorter barbels ( Fig. 6 c), and less deep head and body compared to other chain danios. Principal Component analysis separates D. annulosus from all other Danio with complete lateral line, except that one outlier (NRM 67114, 68.2 mm) clusters with other danios ( Fig. 6 d; Table 3 ). The highest loadings are in head and body depth, dorsal-fin base length, and pectoral- and pelvic-fin lengths ( Table 3 ).

Genetic distance analysis. The sequences (“barcodes”) of all three sequenced specimens of D. annulosus were identical (pairwise p -distance = 0%). In our dataset D. annulosus was most similar to D. catenatus (3.4% pairwise p -distance). A BLAST ( Altschul et al., 1990) nucleotide search of the GenBank non-redundant database (nr) found no exact matches. The closest matches were D. dangila (8% pairwise p-distance) and Danio cf. dangila (8%), followed by an unseparated group of different species of Danio (≥11%).

Entering the D. annulosus barcode into the identification tool at the Barcode of Life database (BOLD) portal (www.boldsystems.org) and searching for a match at the “species” level found no matches. A search of “all barcode records on BOLD” found that the five closest matches in BOLD were Danio aff. dangila (= D. sysphigmatus and D. concatenatus ) (6.6% pairwise p -distance), D. dangila (8.1–8.5%), Danio cf. dangila (= D. assamila ) (8.9%), D. meghalayensis (9.7%) and D. erythromicron (Annandale) (11.5%).

Phylogenetic analysis. The result of the phylogenetic analysis is summarized in Figure 7 . Danio is monophyletic (Bayesian posterior probability, BPP 1.00). Within Danio , there is a trichotomy comprising the monophyletic chain danios (BPP 0.89), and two clades of non-chain danios. The first clade is D. margaritatus (Roberts) + D. feegradei (BPP 0.79), in the other clade (BPP 0.87) D. albolineatus (Blyth) is the sister group to D. kyathit Fang + D. tinwini Kullander & Fang (BPP 0.69). The chain danios comprise two clades. In the first clade (BPP 0.66), D. dangila is the sister of D. meghalayensis + D. assamila (BPP 0.99). In the second clade (BPP 0.99) D. concatenatus + D. sysphigmatus (BPP 1.00) are sister group to a clade comprising D. catenatus + D. annulosus (BPP 1.00).

Figures

FIGURE 1. Danio annulosus: a, holotype, DU 50001, 71.5 mm SL, probable female; preserved in 95 % ethanol; b, paratype, NRM 67114, male, 68.2 mm SL, fixed in formalin; c, paratype, NRM 67114, probable female, 56.0 mm SL, fixed in formalin. All from Bangladesh, Kaptai Lake, Shuvolong Falls.

FIGURE 2. Ventral aspect of a, Danio annulosus, NRM 67114, 68.2 mm SL, with unusually long pectoral fins; b, Danio concatenatus (BMNH 2011.3. 24.50, 61.1 mm SL), to show difference in produced pectoral and pelvic fins between D. annulosus (pectoral fin reaching base of pelvic fin or shorter; pelvic fin not reaching vent) and other chain danios (pectoral fin reaching beyond base of pelvic fin; pelvic fin reaching vent).

FIGURE 3. Collecting sites of chain danios and Danio meghalayensis; modified from Kullander (2015), with Danio annulosus added.

FIGURE 4. Type locality of Danio annulosus, at foot of Shuvolong Falls, at this time almost expired (28 November 2014).

FIGURE 5. Type locality of Danio annulosus, close up of pool at foot of the waterfall where the type series was sampled.

FIGURE 6. Comparative morphometry of Danio annulosus. a – c, pectoral-fin, pelvic-fin and maxillary barbel lengths as percent of SL, plotted against SL, in chain danios; d, Plot of scores of sheared Principal Component 3 against sheared Principal Component 2 from pooled measurements of all species of Danio with complete lateral line.

FIGURE 7. Bayesian majority-rule tree from analysis of mitochondrial COI DNA data from danionine outgroup, chain danios and D. meghalayensis. Values at nodes indicate Bayesian posterior probability estimates. Branch lengths are proportional to number of expected substitutions per site. HT indicates holotype of Danio annulosus. Sequences labeled with DU or NRM museum catalog number, except sequences from Collins et al. (2010), prefixed with RC, and sequences from GenBank with other identifiers. In-group taxon names are colour coded according to geographic occurrence.

Tables

TABLE 2. Morphometry of Danio annulosus. Measurements are in per cent of standard length, except for standard length (in mm). SD, standard deviation; r, Pearson’s correlation coefficient. Linear regression against SL calculated from measurements in mm. HT = Holotype.

N	HT	min	max	mean	SD	a b	r
Standard length (mm) 10	71.5	41.8	71.5	53.2	9.8
Body depth 10	26.2	24.3	28.0	25.5	1.0	-2.242 0.298	0.986
Head length 10	22.5	21.7	23.4	22.7	0.4	0.919 0.209	0.995
Snout length 10	6.7	5.9	6.8	6.5	0.3	0.337 0.059	0.962
Head depth 10	14.7	13.4	15.8	14.8	0.8	0.233 0.144	0.960
Head width 10	12.2	11.7	13.0	12.5	0.4	0.340 0.118	0.986
Upper jaw length 10	9.0	8.2	9.7	9.2	0.4	0.921 0.074	0.969
Lower jaw length 10	10.9	9.7	11.8	11.0	0.6	1.296 0.085	0.946
Orbital diameter 10	6.2	6.2	7.7	7.0	0.5	1.359 0.044	0.965
Interorbital width 10	10.1	9.8	10.5	10.2	0.2	0.366 0.095	0.994
Caudal peduncle length 10	15.2	13.5	16.5	15.3	0.9	1.822 0.118	0.952
Caudal peduncle depth 10	12.4	10.9	13.9	12.0	0.9	-1.847 0.155	0.969
Dorsal-fin base length 10	17.2	15.4	18.0	16.7	0.9	-1.165 0.189	0.972
Anal-fin base length 10	22.0	19.4	23.3	21.5	1.1	-1.948 0.253	0.981
Predorsal length 10	59.4	57.6	61.4	59.7	1.0	1.881 0.561	0.996
Preanal length 10	65.2	64.5	66.9	65.5	0.8	0.017 0.655	0.998
Prepelvic length 10	46.9	44.9	48.3	46.6	0.9	1.426 0.439	0.994
Pectoral-fin length 10	19.4	19.4	25.1	23.2	1.6	2.949 0.175	0.895
Pelvic-fin length 10	13.8	12.8	16.1	14.5	1.0	-0.697 0.158	0.946
Rostral barbel length 10	13.6	13.0	18.0	15.3	1.4	2.743 0.100	0.826
Maxillary barbel length 10	20.0	20.0	24.6	22.9	1.5	3.759 0.156	0.928